monopulse secondary surveillance radar ... - Perner's Contacts

Number 5, Volume VI, December 2011The elevation coverage diagram for 8 elements with spacing of dx = 180 mm isshown in Fig. 5. The solid line shows values without ground reflection effects. Thedashed line depicts ground reflection effects considering very rough assumption forreflection coefficient of Γ = -1, which is approximately valid for θ < 4 0 . Therefore a“null” for angle θ about 3 0 is extremely doubtful. In fact, the absolute value ofreflection coefficient for vertical polarization is sharply decreasing. Moreover, therandom changes, such as terrain variations and vegetation, could be substantial.Fig. 4 - Elevation array factor for N = 8 elements, f =1,06 GHz, dx = 180 mmFig. 5 - Elevation coverage diagram for 8 elements with dx = 180 mm and f =1,06 GHz2. FEED NETWORKThe SSR antenna consists of 216 irradiating elements, arranged into 27 verticalcolumns of 8 elements. The vertical distribution of amplitude and phase creating antennaelevation pattern, common to all three horizontal beams are accomplished by 27 identicalvertical feeders. The vertical feeders are fed by a 3in/27out horizontal feeder generating thethree beams: the sum, the difference and the SLS ones. Due to low insertion loss requirementsthe whole SSR antenna feeder is designed basically as a suspended stripline network.2.1 Vertical feederThe vertical feeder consists of 7 branch line couplers (see fig. 6) of different powerdivisions connected by striplines, providing the appropriate phase and amplitude distribution.Bezoušek, Schejbal: Monopulse Secondary Ssurveillance radar Antenna for Air Traffic Control 25